This is the result of a fairly recent change in requests [1], released 8 Aug. While the enforcement of header-value types is fairly recent, they've documented since 2.0.1 that headers must be byte- or unicode-strings [2], and more recently clarified it in their quick start guide [3]. It looks like this has been addressed in smaug already [4], but I'd expect that you could downgrade requests to 2.10.0 while waiting for a new release of smaug.

This is the result of a fairly recent change in requests [1], released 8 Aug. While the enforcement of header-value types is fairly recent, they've documented since 2.0.1 that headers must be byte- or unicode-strings [2], and more recently clarified it in their quick start guide [3]. It looks like this has been addressed in smaug already [4], but I'd expect that you could downgrade requests to 2.10.0 while waiting for a new release of smaug.